1. Field of Inventive Concepts
The inventive concepts disclosed herein generally relate to non-contact dispensing of liquids, and more particularly, but not by way of limitation, to non-contact micro droplet dispensers and to methods of using thereof.
2. Brief Description of Prior Art
Advances in diagnostics, particularly in point of care testing, have demonstrated great potential in the commercialization and use of miniaturized test instruments and single-use disposable testing devices which include one or more reagents. In some miniaturized test instruments and single-use disposable testing devices, assay reagents are integrated in microfluidic channels in dry reagent microsphere form that provides significant improvements in reagent stability and shelf life at ambient temperatures.
To that end, devices and methods used in the manufacture of lyophilized reagent microspheres are becoming more important as the demand for lyophilized reagent microspheres increases. One approach to manufacture lyophilized reagent microspheres is to dispense micro droplets of liquid reagent ranging in volume from sub-microliter to a few microliters into liquid nitrogen-containing vessels, or onto liquid nitrogen-cooled solid surfaces, to instantly freeze the reagent droplets into reagent microspheres. The frozen reagent microspheres are then lyophilized, or freeze-dried and/or additionally processed before they are sold and/or used with miniaturized testing devices, for example by being packed in microfluidic channels or chambers.
Examples of currently existing devices used to deposit droplets of liquid onto surfaces generally include two broad categories, i.e., contact and non-contact. In the case of contact devices and methods, physical contact between a dispensing probe carrying a droplet of liquid and a target vessel or surface is used to transfer droplets of liquid from the dispensing probe and onto the target surface or into a vessel. Examples of such contact devices include movable elongated pins which are dipped in a liquid and a droplet of the liquid is transferred to the contact surface via capillary action and/or under the force of gravity.
In the case of non-contact dispensing devices and methods, no physical contact between the dispensing device and the target surface is used, instead, positive droplet displacement is utilized such as via syringe-based liquid dispensers, piezoelectric inkjet-type dispensers, or solenoid-based liquid dispensers, which are positioned at a distance above a target surface and used to deposit reagent droplets thereon. Examples of non-contact dispensing devices include piezoelectric inkjet-type devices and syringe-based devices using gaseous bubbles to separate droplets of reagent.
However, several problems exist in the art when attempts are made to use existing contact and non-contact dispensers to dispense reagent droplets into cryogenically cooled vessels or onto cryogenically cooled surfaces. For example, because liquid nitrogen almost instantly freezes reagent that comes into contact with the liquid nitrogen, contact devices and methods of dispensing droplets into liquid nitrogen or onto liquid nitrogen cooled surfaces are impractical, as the reagent tends to freeze inside the dispensing device and cause malfunctions. Further, with piezoelectric inkjet-type non-contact devices, the inkjet nozzle is typically positioned relatively close to the target surface to dispense the reagent droplets reliably, which results in the reagent and/or the inkjet nozzle becoming frozen by the liquid nitrogen, thus rendering such devices impractical and unreliable for use with liquid nitrogen cooled vessels and/or surfaces.
Multiple unsatisfactory attempts have been made to solve these problems. For example, U.S. publication No. 2007/0259348 describes a method for making a lyophilized reagent pellet on a cryogenically cooled, hydrophobic plate, comprising: introducing a liquid into a dispensing tip; positioning the tip in close proximity to the surface, dispensing a droplet from the tip on the surface (contact dispensing); removing the tip away from the surface so the droplet remains in contact with the surface; maintaining the droplet in contact with the surface for such time as the droplet freezes to form a frozen droplet. This method is a contact dispensing method, and it does not address the problem of the dispensing probe or nozzle becoming frozen as the result of the proximity of the liquid nitrogen.
As another example, U.S. publication No. 2003/0170903 describes a non-contact dispensing apparatus which alternately aspirates a liquid reagent and a gaseous fluid into a passageway, forming air gaps between reagent adjacent droplets. When dispensing, it applies a rapid pressure pulse with a predetermined width to the loaded passageway and dispenses liquid without substantial fluid compression of the air gaps. However, the inventors of the instant inventive concepts have tested this method and have found it doesn't work optimally when used with liquid nitrogen and with certain reagents. The air gap may not always separate the liquid droplets from the dispensing orifice; rather, in some cases the gas from the air gap is blown into the liquid reagent droplet and forms bubbles that are frozen with the droplet, which results in sub-optimal formation of the frozen reagent droplets, differing amounts of reagent between frozen droplets, and variations in shape and size of the frozen droplets.
Further, because various reagents have different compositions of proteins, enzymes, and antibodies and vary in viscosity and surface tension, reagent droplets tend to stick to the tip of the dispensing probe or nozzle with varying amounts of adhesive forces. A challenge not adequately addressed by the prior art is to design a dispenser that is configured to handle different reagents, precisely separate micro droplets from the tip of the probe, and reliably inject the micro droplets into a liquid nitrogen vessel or onto a liquid nitrogen-cooled surface.
Accordingly, a need exists in the art for a non-contact reagent micro droplet dispensers and methods configured to dispense micro droplets in cryogenically cooled vessels or onto cryogenically cooled surfaces. It is to such non-contact reagent micro droplet dispensers and to methods of using thereof that exemplary embodiments of the inventive concepts disclosed herein are directed.